1. Field of the Invention
The present invention relates to a method of manufacturing a p-type ZnO semiconductor layer using an atomic layer deposition (ALD) technique and a thin film transistor (TFT) including the p-type ZnO semiconductor layer and, more particularly, to a method of manufacturing a p-type ZnO semiconductor layer including a Zn3N2 layer or a ZnO:N layer formed through a surface chemical reaction between a Zn precursor and an nitrogen precursor on a ZnO thin layer formed through a surface chemical reaction between an oxygen precursor and a Zn precursor, and a TFT including the p-type ZnO semiconductor layer.
The present invention has been produced from the work supported by the IT R&D program of MIC (Ministry of Information and Communication)/IITA (Institute for Information Technology Advancement) [2006-S-079-01, Smart window with transparent electronic devices] in Korea.
2. Discussion of Related Art
In modern times, the demand for electronic devices that can be used any time any place is widespread. Among the electronic devices, thin film transistors (TFTs) are being widely used not only for semiconductor devices but also for display devices, radio-frequency identification (RFID), and sensors. The TFTs may be classified into amorphous silicon (a-Si) transistors and polysilicon (poly-Si) transistors. Also, organic TFTs using organic semiconductors have been developed lately.
In recent years, development of TFTs using transparent oxide semiconductors having wide bandgaps has attracted much attention. Most research has been focused on n-type oxide semiconductor thin layers due to the fact that forming stable p-type oxide semiconductor thin layers is difficult. Specifically, in a p-type oxide semiconductor thin layer, a hole transport path is formed by oxygen 2p orbital. It is typically known that oxygen orbital in an oxide is localized, so that effective hole mass is relatively large to cause a low hole mobility, and valence band minimum is very deep to preclude doping holes.
Currently known p-type oxide thin layers include a ZnO layer doped with nitrogen (N) or phosphorus (P) and a LnCuOCh (Ln: lanthanide, Ch: chalcogen) layer. The LnCuOCh has a disadvantage of low transparency, and the N- or P-doped ZnO layer has low reproducibility and low mobility. Also, in order to manufacture currently published ZnO-based p-type oxide semiconductors, a plasma-enhanced metal-organic vapor phase epitaxy deposition (MOVPED) (Appl. Phys. Lett., 87, 213103, 2005) process or a plasma laser deposition (PLD) (Appl. Phys. Lett., 83, 1128, 2003) process should be performed on a single crystalline substrate, such as a sapphire substrate, at a high temperature of 500° C. However, when a ZnO-based p-type oxide semiconductor thin layer is deposited using a MOVPED or PLD process at a high temperature of 500° C., defects may be generated due to oxygen vacancies formed in the ZnO-based p-type oxide semiconductor thin layer or the remaining Zn ions. Also, when the ZnO-based p-type oxide semiconductor thin layer is deposited using the MOVPED or PLD process, a deposition process should be followed by a high-temperature thermal process in order to activate a dopant. As a result, forming the ZnO-based p-type oxide semiconductor thin layer on a large area is difficult and costly, thus hindering manufacture of low-priced TFTs adequate for ubiquitous environments.